Monday, June 27, 2011

Damselflies!

During that silly freewrite post last week (empty-handed desperation will lead to some strange choices), I mentioned damselflies and posted a picture of one. Let's take a closer look at these little buggers, because they're kinda one of my favorite things about living on this planet.

The one species of damselfly that seems to live around here is Calopteryx maculata -- the ebony jewelwing. Every so often I'll see one or two elsewhere, but there's a pond a few miles down the road where dozens gather on summer afternoons. I keep trying to convince people to take the trip with me, but for some reason they always seem reluctant to sit down in the woods and stare at bugs with me for an hour. Clearly there is something wrong with everyone else in the world.

Look at him. He's almost as cute as a horseshoe crab, and nearly as ancient. Fossils belonging to an extinct subgroup of the order Odanta (which the damselfly shares with its more well-known and vigorous cousin, the dragonfly) have been dated 325,000,000 years old, while the oldest fossils belonging to recognizable members of the Zygoptera suborder (i.e., damselflies) date back 250,000,000 years. Although not quite as Darwin-vintage as our friends in the Limulidae family, Damselflies apparently haven't changed that much in the last couple hundred million years. Their bodies still have weird, outmoded ways of doing things -- mating, for one. You can look it up for yourself, but I will just mention here that it involves the male grabbing the female by the neck with his anus.

Of course, I'm not a biologist or a bug authority of any kind -- in fact, I just now had to look up those numbers and Latin names on this handy web page. Rather than paraphrasing and thereby diluting the information any further, let's quote right from the fountainhead:

Many characteristics distinguish Odonata from other groups of insects -- minute antennae, extremely large eyes (filling most of the head), two pairs of transparent membranous wings with many small veins, a long slender abdomen, an aquatic larval stage (nymph) with posterior tracheal gills, and a prehensile labium (extendible jaws underneath the head). Among living Odonata, there are twenty-five families, mostly dragonflies and damselflies. Of all their characteristics, the easiest way to tell a dragonfly or damselfly from other insects is by the size of the eyes and shape of the abdomen. If the eyes are very large in proportion to the head and the abdomen is long and thin, then it is almost sure to be in Odonata.

While both dragonflies and damselflies belong to the Odonata and share many common features, then are a number of noticeable differences as well. Even before hatching from the egg, differences in morphology of the egg distinguish dragonflies (Anisoptera) from damselflies (Zygoptera). Dragonfly eggs are round and about 0.5 mm long, whereas damselfly eggs are cylindrical and longer, about 1 mm long. Similarly, the nymphs (larvae) of the two groups differ. A larval damselfly abdomen is longer and narrower with three fin-like gills projecting from the end. Dragonfly nymphs are shorter and bulkier, and the gills are located inside the abdomen. The dragonfly nymph expands and contracts its abdomen to move water over its gills, and can squeeze the water out rapidly for a short burst of underwater jet propulsion.....

Both major suborders have large heads with very large compound eyes relative to the rest of their body. Each compound eye is composed of nearly 28,000 individual units (ommatidia), and together the eyes cover most of the head. More than 80% of their brain is devoted to analyzing visual information. By contrast, their antennae are tiny. Their mouths have been adapted for biting, making them efficient hunters. All Odonata have a prehensile labium, which can be extended forward from underneath the head faster than most prey can react, making their bite fatal to prey. The six legs are all located near the head and are seldom used for walking, but are more useful in catching prey and perching on vegetation to rest or lay eggs.

Both dragonflies and damselflies have two pairs of elongated membranous wings with a strong crossvein and many small veins that criss-cross in the wings, adding strength and flexibility to the wings. Both groups also have a characteristic nodus, or notch, in the front edge of each wing. In dragonflies, the rear wings have a broader base and are larger than the front pair. Damselflies, by contrast, have front and hind wings similar in shape, and as a result they fly slower than dragonflies do. Also, dragonflies do not have hinges enabling them to fold their wings together when resting, though damselflies do. This feature of the wings is the key morphological feature distinguishing adult dragonflies from damselflies.

Finding damselflies isn't that tough. Just go to a large wooded area and look for water. It is very important that there be sunlight; damselflies tend to stay put during cloudy weather. What you're keeping an eye open for is a bug that looks like a dragonfly but moves like a butterfly.
Taking pictures of these things isn't easy, unless you have a camera capable of extreme zooming (which I do not). Damselflies are shy. They'll just sit on a leaf and stare at you until you come within about six feet of them. At that point they'll jump and flit about until they're out of reach, land, and resume their staring. (And what cute little cold black eyes they have!) Taking these photos took a few minutes; most of the time the bugs didn't allow me to get close enough to snap a sufficiently detailed photo, but I got lucky every now and then.

They can move fast when they want to, though. If you watch them long enough, you might see a pair of males sparring. They'll approach each other in flight, stop right in front of each other, and hover in place for a few minutes. Their wingflaps become harder and more rapid, and then they'll start darting about like their dragonfly cousins, chasing and ramming into each other. I'm not really sure what's going on when this happens: I've been unable to discern if they're actually biting or inflicting any serious bodily damage on each other. I'm also not sure what the rules on stopping are: sometimes one will tap out and land somewhere, and the other will just flutter off in another direction. Once last year I watched a fight between a pair of males that must have lasted about ten minutes: every time the one removed himself from the fight and landed to take a breather, the other would immediately swoop back down on him and chase him around again. ("Well, animals are a lot like people, Mrs. Simpson....Some of them are just jerks.")

Distinguishing a male from a female is simple, at least as far as ebony jewelwings are concerned. The females are generally a dull, somewhat iridescent blackish-gray color that sometimes contains tints of other colors (I see a lot of purple and green). Their wings will be more transparent than the males', and will have white dots on the high tips.

Though the female has its charm, the male damselfly is comparatively brilliant. Most I've seen are either an emerald green or a deep cerulean, but I suspect that the difference hasn't to do with the individual bug, but on the lighting. I'm fairly positive I've seen a blue damselfly flap into the shade and become green by the time he landed. (I'll post something new if/when I verify this.)

And they're even cuter during their youth, when they squirm underwater as vicious, cannibalistic nymphs!

(I should mention that I did not record this. I've never been able to find any of these things, much less catch them.)

Most of a dragonfly's life is spent in the larval stage where it molts from six to fifteen times. Depending on altitude and latitude, larval development varies from the common one or two years to as many as six years. At that time, the nymph crawls up out of the water and molts one last time, emerging from its old skin as an adult with functional wings. Unlike butterflies and beetles, dragonflies and damselflies do not have an intermediate pupal stage before becoming an adult. Because of this, Odonata are said to be hemimetabolous, or undergo an "incomplete" or "gradual" metamorphosis.

Dragonflies and damselflies begin their lives as nymphs, living underwater for a year of more....The nymphs are not as brightly colored as the adults, but are well camouflaged predators who ambush their prey.

And I haven't got much else. Those first two pictures at the top are from a year or two ago; today I went out to collect some more (for your viewing pleasure). You can click on any of them for a higher-resolution version.

On the way to the pond I met a dapper little mushroom:

And when I arrived, I found this gentleman sunning himself in a bush:

There was also a huge turtle floating in the middle of the pond, but he went under before I could get a snapshot of him.

I enjoy my hobbies, but they're probably one of the reasons I have such a hard time getting dates.